1. Field of the Invention
The invention concerns a process for the operation of nuclear reactors, particularly gas-cooled reactors, and a control system for nuclear reactors for carrying out the process.
2. Description of the Prior Art
Nuclear power plants such as gas-cooled nuclear reactors having a reactor core, a turbine, a compressor and a heat exchanger are known in the art. Often these power plants will possess one or more circuits for the transfer of the energy from the nuclear reaction and conversion of such energy to drive turbine generations for example. These circuits may comprise the turbine assembly, gas lines, coolers, recuperators and the like for effective operation of the power plant. Complex arrangements are often necessary to adequately house the reactor core and to carry out its operation under regulated and controlled conditions for the conversion of energy on an economical basis during continued operation of the power plant.
In addition to devices for the regulation and control of the usual operation processes, nuclear reactors are also conventionally equipped with safety system which shut the reactor down when fault conditions arise. In one such system, a rapid shut-down or scram of the reactor takes place first and, if the fault cannot be obviated within a predetermined time interval, a long-term or full shut-down occurs. For the detection and measurement of the fault parameters-essentially neutron flux, reactor period, temperature and pressure-a so-called reactor protection system is often employed. Being a component of the safety system, it consists of instrumentation for the detection of faults, limiting value indicators and control devices. In a conventional process and neutron flux in the core is measured and, when it exceeds a certain threshold value, a rapid shutdown is effected. As an alternative process, it is also known to utilize the measured temperature of the coolant or operational pressures as fault parameters for reactor shut-down.
In order to achieve the greatest possible safety and reliability, the reactor protection system is, as a rule, arranged in a redundant manner, i.e. several identical signals are necessary for bringing about a shut-down. For safety reasons, however, the signals of different fault parameters are not compared with each other: rather, for the initiation of a reactor shut-down it suffices if one fault magnitude gives a signal exceeding the threshold value.
The drawback of this known process and reactor protection system is that the reactor is shut down even in the event of relatively unimportant small faults, e.g. from subordinate control loops, or faulty functioning which cannot lead to any serious impairment of components and which can be eliminated or corrected without particular trouble, or in the event of a strong deflection of the measuring instruments, or in the event of the short-term overshoot of the control parameters. Although the reactor may be started up again directly after the fault or overshoot comes to an end, nevertheless, temperature cycles that are harmful to components of the reactor cannot be avoided.